Shock (circulatory)


Shock is the state of insufficient blood flow to the tissues of the body as a result of problems with the circulatory system. Initial symptoms of shock may include weakness, elevated heart rate, fast breathing, sweating, anxiety, and increased thirst. This may be followed by confusion, unconsciousness, or cardiac arrest, as complications worsen.
Shock is divided into four main types based on the underlying cause: hypovolemic, cardiogenic, obstructive, and distributive shock. Hypovolemic shock, also known as low volume shock, may be from bleeding, diarrhea, or vomiting. Cardiogenic shock may be due to a heart attack or cardiac contusion. Obstructive shock may be due to cardiac tamponade or a tension pneumothorax. Distributive shock may be due to sepsis, anaphylaxis, injury to the upper spinal cord, or certain overdoses.
The diagnosis is generally based on a combination of symptoms, physical examination, and laboratory tests. A decreased pulse pressure or a fast heart rate raises concerns.
Shock is a medical emergency and requires urgent medical care. If shock is suspected, emergency help should be called immediately. While waiting for medical care, the individual should be, if safe, laid down. The legs should be raised if possible, and the person should be kept warm. If the person is unresponsive, breathing should be monitored and CPR may need to be performed.

Signs and symptoms

The presentation of shock is variable, with some people having only minimal symptoms such as confusion and weakness. While the general signs for all types of shock are low blood pressure, decreased urine output, and confusion, these may not always be present. While a fast heart rate is common, in those on β-blockers, those who are athletic, and in 30% of cases of those with shock due to intra abdominal bleeding, heart rate may be normal or slow. Specific subtypes of shock may have additional symptoms.
Dry mucous membrane, reduced skin turgor, prolonged capillary refill time, weak peripheral pulses, and cold extremities can be early signs of shock.

Low volume

is the most common type of shock and is caused by insufficient circulating volume. The most common cause of hypovolemic shock is hemorrhage ; however, vomiting and diarrhea are more common causes in children. Other causes include burns, as well as excess urine loss due to diabetic ketoacidosis and diabetes insipidus.
ClassBlood loss ResponseTreatment
I<15% min. fast heart rate, normal blood pressureminimal
II15–30% fast heart rate, min. low blood pressureintravenous fluids
III30–40% very fast heart rate, low blood pressure, confusionfluids and packed RBCs
IV>40% critical blood pressure and heart rateaggressive interventions

Signs and symptoms of hypovolemic shock include:
The severity of hemorrhagic shock can be graded on a 1–4 scale on the physical signs. The shock index is a stronger predictor of the impact of blood loss than heart rate and blood pressure alone. This relationship has not been well established in pregnancy-related bleeding.

Cardiogenic

is caused by the failure of the heart to pump effectively. This can be due to damage to the heart muscle, most often from a large myocardial infarction. Other causes of cardiogenic shock include dysrhythmias, cardiomyopathy/myocarditis, congestive heart failure, myocardial contusion, or valvular heart disease problems.
Symptoms of cardiogenic shock include:
is a form of shock associated with physical obstruction of the great vessels of the systemic or pulmonary circulation. Several conditions can result in this form of shock.
Many of the signs of obstructive shock are similar to cardiogenic shock, although treatments differ. Symptoms of obstructive shock include:
  • Abnormal heart rhythms, often a fast heart rate.
  • Reduced blood pressure.
  • Cool, clammy, mottled skin, often due to low blood pressure and vasoconstriction.
  • Decreased urine output.

    Distributive

is low blood pressure due to a dilation of blood vessels within the body. This can be caused by systemic infection, a severe allergic reaction, or spinal cord injury.
Although not officially classified as a subcategory of shock, many endocrinological disturbances in their severe form can result in shock.
Shock is a common end point of many medical conditions. Shock triggered by a serious allergic reaction is known as anaphylactic shock, shock triggered by severe dehydration or blood loss is known as hypovolemic shock, shock caused by sepsis is known as septic shock, etc. Shock itself is a life-threatening condition as a result of compromised body circulation. It can be divided into four main types based on the underlying cause: hypovolemic, distributive, cardiogenic, and obstructive. A few additional classifications are occasionally used, such as endocrinologic shock.

Pathophysiology

Shock is a complex and continuous condition, and there is no sudden transition from one stage to the next. At a cellular level, shock is the process of oxygen demand becoming greater than oxygen supply.
One of the key dangers of shock is that it progresses by a positive feedback loop. Poor blood supply leads to cellular damage, which results in an inflammatory response to increase blood flow to the affected area. Normally, this causes the blood supply level to match with tissue demand for nutrients. However, if there is enough increased demand in some areas, it can deprive other areas of sufficient supply, which then start demanding more. This then leads to an ever escalating cascade.
As such, shock is a runaway condition of homeostatic failure, where the usual corrective mechanisms relating to oxygenation of the body no longer function in a stable way. When it occurs, immediate treatment is critical in order to return an individual's metabolism into a stable, self-correcting trajectory. Otherwise the condition can become increasingly difficult to correct, surprisingly quickly, and then progress to a fatal outcome. In the particular case of anaphylactic shock, progression to death might take just a few minutes.